Engine emission control is one of the important technologies installed in modern motor vehicles. In order to clean exhaust emissions through the exhaust pipe of an internal combustion engine, a catalyst converter is normally provided in the exhaust pipe. Catalyst converters, each of which consists of a catalyst and a metal carrier carrying it, are characterized to activate with their temperatures equal to or higher than an activation temperature, and, in the activated state, oxidize particular components in the exhaust emissions. Thus, when the temperature of a catalyst converter provided in the exhaust pipe is lower than its activation temperature during, for example, engine start-up, heating the catalyst converter to activate the catalyst converter as soon as possible is required. As an example of how to heat a catalyst converter, U.S. Pat. No. 5,758,492 corresponding to Japanese Examined Patent Publication No. 3602614 discloses an electrically heated catalyst converter, referred to simply as an “EHC converter”, which supplies current to the metal carrier of the EHC converter to thereby heat the metal carrier.